This invention relates to a telescopic apparatus, and particularly to a kind of an adjustable telescopic apparatus having a master and a slave pipe body combined together with an oil and an air portion being divided therein for being optionally adjusted to control the moving speed and force required to collapse the slave pipe body into the master pipe body so as to obtain the desired telescopic operations.
Conventionally, telescopic devices are generally classified into spring-operated types and air-compression types. In the former type, a helical spring is usually installed in a double tubing arrangement which, when pressed by an external force, one member of said double tubing arrangement will contract against the helical spring being compressed therein and, when the external force is released, the compressed spring will expand to push said one member of the double tubing arrangement to extend therefrom. In the latter type, compressed gas is used to effect telescopic operations. As shown in FIGS. 1 and 2, a known lift rod, such as that used in a car trunk lid, includes a pipe (A) and a piston rod (B). One portion of the pipe (A) is filled with gas (usually nitrogen) and some lubricating oil. A connecting member Al provided at an end of the pipe (A) enabling said pipe (A) to be fastened on a car body or door. Another portion of the pipe (A) is provided with a first and a second fixed seal ring A2, A3 placed one in front of the other, at the end thereof. A flexible air-tight ring (usually of a rubber material) A4 is arranged between the two seal rings Al, A2 around the pipe (A) with a pair of circular recesses A21, A31 defined between said two seal rings A2, A3 for obtaining an air-tight effect therewith. The piston rod (B) includes a round piston B1 at one end with an opening B2 formed therein and a coupling member B3 extending out from the sealed end of the pipe (A).
The operations of this known lift rod is as shown in FIG. 2. When a user pushes down the car trunk lid, which is supported by said lift rod, causing a downward pressing force (F) to be applied to the piston rod (B), which is moved into the pipe (A), a first and a second spaces (I), (II) will be created therein. At this stage, the gas pressure PI in the first space (I) will be gradually greater than the gas pressure PII in the second space (II) so that the gas in the first space (I) will be forced to pass through the opening B2 in said piston B1 and enter into the second space (II), equalizing the gas pressure in both spaces (I) and (II), (i.e. PI=PII), so that the lift rod is kept in a retracted condition. When the pressing force (F) is released from said lift rod, i.e. when the car trunk lid is open, the gas pressure in the second space (II) of pipe (A) will be greater than that of the first space (I) of the pipe (A), the piston rod (B) will be gradually moved out from said pipe (A) since the opening B2 of said piston B1 is not big enough to quickly allow the gas from the second space (II) to pass therethrough, resulting in the desired slow lifting operation.
A common drawback suffered by the above-described prior art is that since the extension and the speed of the stretching resistance and retracting speed thereof are normally fixed at the site of manufacture, application of said prior art is very limited, unless various said stretching resistances and retracting speeds are provided in conformity with various needs of the prior art, often causing a considerable inconvenience.